Synthesis, crystal structure, and photophysical properties of dimethyl 7-oxa-2a1-azabenzo[b]cyclopenta[pq]pleiadene-1,2-dicarboxylate – novel fused oxazapolycyclic skeleton

Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings

“…Although the intramolecular free-radical cyclization is widely used for the synthesis of heteroaromatic compounds [23][24][25][26], only a few examples of the successful use of radical cyclization for the synthesis of pyrrole-containing fused heteroaromatics are known in the literature [23][24][25][26][27][28][29][30]. We initiated our study with the attempts to carry out the cyclization of 4-(2bromophenyl)pyrrole 1a under standard radical cyclization conditions (azobisisobutyronitrile (AIBN)/Bu 3 SnH), which previously had been successfully used for the cyclization of 2-bromophenyl-substituted pyrroles into 7-oxa-2a 1azabenzo[b]-cyclopenta[pq]pleiadenes [30]. However, an attempt to use AIBN/Bu 3 SnH for the cyclization of pyrrole 1a to compound 3a only led to a tarring of the reaction mixture, regardless of the temperature (70-110 °C, MeCN) and the protocol for mixing the reagents (Scheme 2).…”

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…In 2017, Khlebnikov et al reported the construction of the indole-fused dibenzoxazepine derivative 298.3 ( Scheme 298 ). 564 The aziridine 298.1 reported by the same group was subjected to cycloaddition with dimethyl maleate in refluxing toluene to give the pyrrolidine 298.2 stereoselectively in 91% yield. Exposure of 298.2 to AIBN and tributyltin hydride at a high temperature brought about the free radical cyclization that led to the indole-fused dibenzoxazepine 298.3 in 56% yield.…”

“… a Reagents and conditions: (a) toluene, reflux, 8 h; (b) AIBN (2.2 equiv), Bu 3 SnH (0.5 equiv), toluene, 80 °C, 7 h; (c) AIBN (1.1 equiv), Bu 3 SnH (0.5 equiv), toluene, 80 °C, 4 h. …”